A process for forming populations of fine particles or molecules on a substrate with specified distribution forms and distribution densities is increasingly important in many fields.
In tissue engineering research, for instance, cells are cultured and aggregated three-dimensionally to study the functions of cells in vitro. According to a known technique, cells are cultured in a floating condition in a vessel the surface of which is specially treated to prevent cell adhesion. The cells are then self-aggregated to form small globules through the action of the oscillation of fluids and the adhesive force of the cells. In another method, cells are cultured and self-organized in a gel where they can move freely. With these techniques, aggregation takes place randomly and the size of the formed aggregates varies widely from tens to several hundreds of micrometers even though the same vessel is used.
Techniques to achieve cell aggregation to a desired size include (1) using a small cylindrical vessel and (2) using a substrate with a number of small through-holes. In these methods, a suspension is added to such a substrate with micro-holes on its flat surface. The cells settle out on the substrate in the form defined by the hole configuration, eventually enabling researchers to achieve a result with the desired cell aggregates.
The process of forming populations of fine particles or molecules with a specified distribution form and distribution density is also very important when adding gene transfer agents or other biochemical reagents locally into cells being cultured with a specified concentration that induces cell differentiation. In the electronics industry, technologies to deposit metal nanoparticles and other functional materials on substrates with specified patterns are actively being studied as a new printed circuit board fabrication process.
Examples of patent publications related to the above technologies include:    Patent literature 1: Patent Application Publication No. 2006-055069    Patent literature 2: Patent Application Publication No. 2006-122012